<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>

        .container {
            width: 500px;
            height: 500px;
            background-color:grey;
            display: flex;
            flex-direction: column;
            justify-content: flex-center;
            align-items: flex-end;
        }
        .box1{
            width: 500px;
            height: 500px;
            background-color:red;
            flex: 1;

        }

        .box2{
            width: 500px;
            height: 500px;
            background-color: green;
           flex: 2;
    
        }

        .box3{
            width: 500px;
            height: 500px;
            background-color:blue;
        }
    </style>
</head>

<body>
    <div class="flex-container">
        <div class="box1"></div>
        <div class="box2"></div>
        <div class="box3"></div>
    </div>
</body>

</html>